The present invention relates generally to systems for measuring haze in transparencies, such as aircraft windscreens, canopies, windows or the like, and more particularly to system and method for in situ measurement of haze in a transparency utilizing an annular light source.
A transparent material, especially plastic, has a tendency to scatter part of the light that is incident upon it. The effect of this scattered light is a veiling luminance (brightness) or haze that is visible in the transparency, and causes loss of contrast of objects viewed through the transparency. The American Society for Testing and Materials (ASTM) has a standard test method (D-1003) based on a National Institute of Standards and Technology circular to measure haze in transparent parts. This procedure requires collimated light to be projected through the part to an aperture in an integrating sphere. The collimated light source and integrating sphere must be disposed on opposite sides of the part and must be structurally interconnected in order to allow alignment between source and sphere, which limits the size and configuration of parts that can be tested using this method. A reliable haze test method is therefore required which provides haze values similar to the ASTM procedure but which does not require equipment components on both sides of the part to be tested (such as in situ tests of aircraft windscreens). A method described in U.S. Pat. No. 4,687,338 to Task et al requires equipment on one side only of the transparency but does not include effective means for reducing or determining directionality effects of light scatter in the transparency.
The invention solves or substantially reduces in critical importance problems with prior art testing methods as just described by providing system and method for accurate in situ measurement of haze in transparent parts, such as aircraft windscreens, wherein components of the system are required only on one side of the transparency being tested. The invention includes a distributed annular light source for illuminating the transparency and for reducing directionality effects on the haze measurement. A detector/lens combination measures luminance of the transparency along the axis of the annular light source.
The invention has substantial utility in monitoring aircraft transparencies for replacement at unsafe haze levels or in quality control associated with transparency manufacture.
It is therefore a principal object of the invention to provide system and method for measuring haze in a transparency.
It is another object of the invention to provide system and method for measuring haze in a transparency through illumination of the transparency and measurement of the haze therein from a single side of the transparency.
It is a further object of the invention to provide an inexpensive system and method for in situ measurement of haze in a transparency using an annular light source.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.